Numerous control systems utilizing photocells or other type detectors have been devised for sensing the position of a material loop in the textile, steel and magnetic tape environs, and depending upon the position of the material in the loop, providing a signal to one of the machines to set the speed of the machine. Generally speaking, the position of the material, web, or the like has been detected intermittently or continuously to provide a proportional output from a photocell. The material handling machine would thus be corrected by an amount indicated as necessary by the detectors.
Such prior art systems have normally employed variable speed drive units for the web handling machine to be controlled with a direct input through the drive being received from the photocell. Constant adjustment of the loop may thus be necessary to compensate for adjustment overages as the result of the detection at the photocell. Over compensation, of course, causes a controlled machine or slave to be sped up from an abnormally slow speed to a greater than required speed or the reverse. A reverse compensation must then be made to return the speed toward a proper rate. Large changes are jumpy in both directions, and preclude a smooth drive system for the web handling equipment. Certainly, with overall conditions being desirable for smoothness and optimum operability, a smooth web drive is quite important, especially for a web that is susceptible to distortion or destruction due to abrupt changes in speed or direction. Hence, it is very advantageous to afford a system where the modifications to the drive speeds of the slave are more accurate and constantly approach an optimum situation, where large speed changes are generally not involved.
In general, especially where web handling equipment comprises two independent machines, operation of the slave machine is controlled by the master machine with a web loop being located between the two, independent machines. To provide a proper loop control, prior art techniques have sometimes included modification of the internal controls of the slave, to provide a similar system to that found in the master machine. This approach is disadvantageous, in that, the internal controls of the slave must be first studied and known to permit proper modification to achieve suitable input from the master. A large number of different drive systems per se, and control units for drive systems, present problems insofar as design of a standardized system is concerned. Moreover, once the slave controls have been modified to permit association with the master for automatic operation, the slave cannot then be returned to manual, separate operation without readjustment.
The present invention affords a system that permits ready synchronization of a master and slave machine without internal modification of either. Further, the present system is quite stable, and may be utilized in virtually any process having a flow of material between two machines. Disadvantages as discussed above are virtually absent when the present system is utilized.
The present invention, both as to the method and apparatus, represents improvements over the prior art. Exemplary of the prior art are U.S. Pat. Nos. 2,888,259 to Taylor et al; 2,900,143 to Bandy et al; 3,047,198 to Long; 3,177,749 to Best et al; 3,236,429 to Klein; 3,240,411 to Zarleng; 3,250,480 to Jacoby; 3,435,245 to Lee; 3,550,878 to Crisp et al; 3,656,855 to Collart et al; and 3,676,009 to Brendemuehl.